JPH05323117A - Polarizing device and projection type display device using same - Google Patents

Abstract

PURPOSE:To provide the inexpensive, compact polarizing device by improving the reliability of the incidence-side polarizing plate of, specially, the projection type display device as to the projection type display device which uses a light valve and the polarizing device which uses the incidence-side polarizing plate. CONSTITUTION:Incidence-side prisms 11 and projection-side prisms 12 having polarized light selective mirror surfaces 14 forming an air layer 13 are arranged. The polarized light selective mirror surface 14 is formed by sticking an optical thin film 17 which has a higher refractive index than the prism on the air layer formation surface of the prism and has such characteristics that when natural light is made incident, light close to linear polarized light is projected. The thickness of the polarizing device is reduced because of a prism type forming the air layer 13 and having the polarized light selective mirror surfaces 14 slanting to the optical axis, and the optical thin film 17 is stuck on a glass substrate 16, so the heat resistance and light resistance are plate is used for the projection type display device, the temperature rise of the incidence-side polarizing plate can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing device that emits light close to linearly polarized light when natural light enters, and a projection type display device using the polarizing device.

[0002]

2. Description of the Related Art In order to obtain a large screen image, a method of forming an optical image according to an image signal on a light valve, irradiating the optical image with light, and enlarging and projecting it on a screen by a projection lens is better than before. Are known. Recently, attention has been paid to a projection display device using a liquid crystal display device as a light valve.

A schematic structure of a projection type display device using this liquid crystal display device is shown in FIG. The light emitted from the light source 1 passes through the liquid crystal display device 2 and enters the projection lens 3. The liquid crystal display device 2 includes a liquid crystal cell 4, an incident side polarization plate 5, and an emission side polarization plate 6. The liquid crystal cell 4 is one in which a twisted nematic liquid crystal 9 is sealed between two glass substrates 7 and 8, and matrix transparent electrodes are provided on the liquid crystal layer side surfaces of the glass substrates 7 and 8, respectively. The polarization axes of the incident side polarization plate 5 and the emission side polarization plate 6 are orthogonal to each other. When no voltage is applied to the transparent electrode, the linearly polarized light emitted from the incident side polarization plate is 90 ° in the liquid crystal cell 4 due to the optical rotatory power.
Since it rotates, the transmittance becomes maximum. When a voltage is applied, the optical rotatory power decreases according to the voltage, and the transmittance decreases. In this way, an optical image corresponding to the video signal is formed on the liquid crystal display device 2 as a change in transmittance, and this optical image is enlarged and projected on the screen 10 by the projection lens 3.

[0004]

With the structure shown in FIG. 11, the incident side polarizing plate 5 has a transmittance of about 40 for natural light.
%, And most of the non-permeable components are absorbed and become heat.
When the temperature of the incident side polarization plate 5 rises, the temperature of the liquid crystal cell 4 also rises due to radiation. The polarizing plate and liquid crystal have limited heat resistance and light resistance, and the polarization degree of the polarizing plate deteriorates due to intense light irradiation.
Since the image quality of the liquid crystal cell deteriorates, it is difficult to maintain a high quality projected image for a long period of time.

In response to this problem, generally, the liquid crystal cell 4,
Although the polarizing plates 5 and 6 are cooled by a cooling fan, noise of the cooling fan poses a problem. If linearly polarized light is made incident on the incident side polarizing plate 5, the amount of light absorption of the incident side polarizing plate 5 is reduced. Therefore, a method of disposing a polarizing beam splitter immediately after the light source 1 (US Pat. No. 4,464,018) Gazette) has been proposed. In addition, a polarizing beam splitter using a liquid instead of glass (see US Pat. No. 4,464,019).
No.) is also proposed. However, the polarization beam splitters proposed hitherto all have a large volume, and there is a problem that it is difficult to assemble a set compactly.

Further, Glan-Thompson prisms and Glan-Taylor prisms, which are polarizers utilizing the birefringence of a crystal, are very expensive and difficult to adopt.

It is conceivable to arrange a front polarizing plate immediately after the light source. Since the front polarizing plate is not required to have a high degree of polarization as much as the incident side polarizing plate, the front polarizing plate has a higher heat resistance than the iodine type polarizing plate. A method using a dye-based polarizing plate which is advantageous in light resistance and light resistance (Japanese Patent Laid-Open No. 63-4217) has been proposed. However, the front polarizing plate suppresses the heat generation of the incident side polarizing plate, but the temperature is high near the light source, and the heat resistance of the front polarizing plate is
It is difficult to adopt because it exceeds the limit of light resistance.
In any case, it is difficult to obtain a bright and high-quality projected image because a new problem arises when trying to overcome the heat resistance and light resistance limits of the incident side polarization plate.

[0008]

In order to achieve this object, a polarizing device of the present invention is provided with an incident-side prism in which light is incident substantially vertically and then is obliquely emitted, and light emitted from the incident-side prism to an air layer. Is formed by an exit side prism that emits light in a substantially vertical direction after obliquely entering, and the refraction index higher than the refraction index of the entrance side prism and the exit side prism is formed on each surface of the entrance side prism and the exit side prism forming an air layer. A polarization-selective mirror surface with an optical thin film having a refractive index, and each polarization-selective mirror surface with respect to the optical axis so that the transmittance is approximately maximum for P-polarized light incident along a predetermined optical axis. It is a slant.

The polarizing device of the present invention can also be used by disposing at least one parallel plane plate between the entrance side prism and the exit side prism and forming at least two or more air layers. Further, the polarizing device of the present invention can also be arranged and used so that the cross section of the air layer formed by the plurality of incident-side prisms and the exit-side prism is zigzag.

Further, the polarizing device of the present invention can be used in a projection type display device using a light valve.

[0011]

The reflectance when light passes through the optical thin film from the air and is obliquely incident on the substrate can be considered separately for the two cases of S-polarized light incidence and P-polarized light incidence, and S-polarized light reflectance R _S , P polarized light reflectance R _P can be expressed as follows.

[0012]

[Equation 9]

[0013]

[Equation 10]

[0014]

[Equation 11]

[0015]

[Equation 12]

[0016]

[Equation 13]

[0017]

[Equation 14]

[0018]

[Equation 15]

Where r _S1 , r _S2 , r _P1 and r _P2 are reflection coefficients of the boundary surface formed by the optical thin film, the subscript S is S-polarized light incident, the subscript P is P-polarized light incident, and the subscript 1 is external. The interface between the medium and the optical thin film, the subscript 2 indicates the interface between the optical thin film and the substrate. d is the film thickness of the optical thin film, and λ is the dominant wavelength of the light beam in the air. n ₀ is the refractive index of the external medium, n ₁ is the refractive index of the optical thin film, n ₂ is the refractive index of the substrate, θ ₀ is the incident angle of the light ray incident on the optical thin film from the external medium, and θ ₁ is the refraction in the optical thin film. The angle θ ₂ is the refraction angle in the substrate, and from Snell's law,
The following equation holds.

[0020]

[Equation 16]

From the above equation, it is understood that when the incident angle θ ₀ is given, R _S and R _P are functions of sin ² (γ / 2), and take different values depending on the film thickness d and the wavelength λ. The external medium is air (n ₀ = 1), and the refractive index of the substrate is n ₂ = 1.52.
When n ₁ > n ₂ , R _S and R _P exist between two curves (hatched areas) as shown in (FIG. 1). One of the two curves is sin ² (γ
/ 2) = 1 and the other is sin ² (γ / 2) = 0
Is the case. The latter curve is equal to the reflectance at the interface between the substrate without the optical thin film and the air.

The two curves of R _P are 0 at certain incident angles θ _A and θ _B , and the two curves intersect at an incident angle θ _C. From (Fig. 1), R _P
It can be seen that the incident angle θ ₀ that minimizes _R is between θ _A and θ _B , and that when θ _A ≦ θ ₀ ≦ θ _B , R _S is considerably higher than R _P. Since it can be considered that the transmittance is 100% minus the reflectance, the incident angle θ _{0 at} which the P-polarized light transmittance is maximum exists between θ _A and θ _B , and θ _A ≦ θ ₀ ≦ θ _B
At this time, the P polarized light transmittance becomes close to 100%, and the S polarized light transmittance becomes considerably smaller than 100%. For increasing R _S , the incident angle should be θ _C rather than θ _A ≦ θ ₀ ≦ θ _C.
It is desirable to select ≦ θ ₀ ≦ θ _B.

From FIG. 1, if the incident angle θ ₀ is θ _B and sin ² (γ / 2) = 1, then R _P becomes 0%,
It can be seen that R _S has a very high value. As conditions for this, the following two are derived from (Equation 10), (Equation 13), (Equation 14), (Equation 15).

[0024]

[Equation 17]

[0025]

[Equation 18]

From (Equation 16) and (Equation 17), the incident angle θ _{0 in} air is as follows.

[0027]

[Formula 19]

[0028]

[Equation 20]

The phenomenon in which R _P is 0%, R _P is similar to the phenomenon which becomes 0% at an incident angle that is at the interface two different media having refractive index. The incident angle or refraction angle in this case is generally called Brewster's angle. Θ _{0 in} (Equation 17) and (Equation 19) will be referred to as a pseudo Brewster angle in distinction from a general Brewster angle.
R _S when the conditions of (Equation 17) and (Equation 18) are satisfied
Is as follows by using (Equation 9).

[0030]

[Equation 21]

When n ₀ = 1 in (Equation 21), n ₁ is n ₂
More, that R _S increases seen larger than the.
That is, in order to increase R _S , it is preferable to wear an optical thin film having a refractive index as high as possible as compared with the glass substrate.

The same applies to the case where light obliquely enters the optical thin film from the substrate and exits to the external medium, and the condition that R _P is 0% is that when (Equation 17) and (Equation 18) are satisfied. It holds. The pseudo Brewster angle θ _{2 in} this case is also (Equation 1
From (6), (Equation 17), and (Equation 20), the following is obtained.

[0033]

[Equation 22]

Similarly, R _S can also be obtained from (Equation 21). Increasing n ₁ to reduce the S-polarized light transmittance increases the incident angle θ ₀ in the air, and the plate-type polarization-selective mirror has an extremely long thickness in the optical axis direction. The polarizing device of the present invention is a prism type provided with a polarization-selective mirror surface that forms an oblique air layer. Light enters the prism substantially perpendicular to the optical axis, and then the polarization-selective mirror surface from the substrate side. Incident on the other polarization-selective mirror surface at an angle of incidence θ ₂ and then becomes oblique in the air layer.
Since the light is incident at ₀ and is emitted from the prism into the air substantially vertically, the angle of inclination of the polarization-selective mirror surface may be θ ₂ , and in general θ ₂ <θ ₀ , It requires less space in the axial direction, which is very effective in making the polarizing device compact. As a result, the projection display device can be compactly assembled using this polarizing device.

As is apparent from the above, the advantages of the polarizing device of the present invention are that it is inexpensive, has excellent heat resistance and light resistance, and is thin. Further, an advantage of the projection type display device using the polarizing device of the present invention is that a bright and high quality projection image can be displayed for a long period of time, the cost is low, and the set is compact.

[0036]

Embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 2 shows the construction of an embodiment of the polarizing device which is the basis of the present invention.
Reference numeral 12 is an exit side prism, 13 is an air layer, and 14 is a polarization selective mirror surface. The air layer 13 is formed substantially in parallel by the spacer 15 so as to have a thickness of about 0.1 mm.

The configuration of the polarization-selective mirror surface 14 (FIG. 3)
Shown in. An optical thin film 17 is provided on the glass substrate 16. It is desirable that the optical thin film 17 has a low absorption and a high refractive index. Table 1 shows materials that can be used as the optical thin film 17 in the visible light region and their refractive indexes. Among these, titanium dioxide, cerium dioxide, or zinc sulfide having the highest refractive index of 2.3 is preferably used as the optical thin film 17.

[0039]

[Table 1]

The incident angle θ ₂ from the glass substrate 16 to the optical thin film 17, or the incident angle θ ₀ from the air to the optical thin film 17.
May satisfy (Equation 16) and (Equation 17), and the thickness d of the optical thin film 17 may satisfy (Equation 18) at the dominant wavelength. Assuming that the external medium is air, the optical thin film 17 is titanium dioxide, and the substrate 16 is optical glass, as shown in (Table 2), when n ₀ = 1, n ₁ = 2.3, and n ₂ = 1.52,
θ ₀ = 72.2 °, θ ₁ = 24.5 °, and θ ₂ = 38.8 °. If the dominant wavelength is λ = 500 nm, d = 59.
It becomes 7 nm. At this time, R _S = 0.7 from (Equation 21)
It will be 18.

[0041]

[Table 2]

FIG. 4 shows the spectral transmittance characteristics when parallel light is incident on the polarizing device shown in FIG. 2 with the configuration shown in Table 2. The incident angles θ ₀ and θ ₂ are θ ₀ = 72.2 ° and θ ₂ = 38.8 °, which are pseudo Brewster angles. In the wavelength region of 400 to 700 nm, the P polarized light transmittance becomes 95% or more and the S polarized light transmittance becomes 10% or less. Since there are two surfaces of the same optical thin film, the S polarized light transmittance becomes very small. It can be seen from (FIG. 4) that the polarizing device shown in (FIG. 2) can efficiently extract light close to linearly polarized light when natural light enters.

The S-polarized light transmittance of the polarizing device is less than about 20%.
If not, the effect of suppressing the temperature rise of the incident side polarization plate is sufficient.
It is confirmed that it is recognized. S-polarized light transmission of the polarizing device
In order to make the ratio smaller than about 20%, the polarization selective mirror 1
S-polarized reflectance per surface is R _S If ≦ 0.55
N, n₀= 1, n₂= 1.52, from (Equation 21)
n₁ The condition of ≧ 2.0 is required. Thin film material in this case
Is titanium dioxide, cerium dioxide, zinc sulfide, pentoxide
Ditantalum, zirconium dioxide, diindium trioxide
Aluminum, zinc oxide, or hafnium dioxide.
Thus, the optical properties and durability will be good.

As shown in FIG. 5, the incident side prism 1
1, a plane parallel plate 18 is arranged between the exit side prisms 12, and the air layer 13 formed by the polarization selective mirror surface 14 is formed into two layers.
In other words, the S-polarized light transmittance can be further reduced. In order to make the S-polarized light transmittance in this case smaller than about 20%, it suffices that R _S ≦ 0.33, where n ₀ = 1 and n ₂ =
If it is set to 1.52, the condition of n ₁ ≧ 1.7 is obtained from (Equation 21). The thin film material in this case is titanium dioxide,
If any one of cerium dioxide, zinc sulfide, tantalum pentoxide, zirconium dioxide, diindium trioxide, zinc oxide, hafnium dioxide, yttrium trioxide, and silicon monoxide is used, good optical characteristics and durability will be obtained. As the number of surfaces of the polarization selective mirror increases, the S polarized light transmittance can be reduced.

Further, as shown in (FIG. 6) and (FIG. 7), the entrance side prism 11, the exit side prism 12, or the plane parallel plate 18 is divided into a plurality of parts, respectively, and the air layer 13 has a zigzag cross section. With this arrangement, the thickness in the optical axis direction becomes thin, and the polarizing device can be made more compact.

Unwanted S-polarized light reflected by the polarization-selective mirror 14 may emerge obliquely from the polarizing device and enter the incident-side polarization plate. In this case, the surface of the incident side prism 11 and the side of the exit side prism through which P-polarized light is transmitted is sanded and black-painted to eliminate unnecessary S.
The polarized light may be diffused or absorbed.

FIG. 8 shows the construction of an embodiment of a projection type display device using the polarizing device of the present invention as a front polarizing device. 32 is a light source, 33 is a front polarizing device, and 34 is an incident light. Side polarizing plate, 35 is a liquid crystal cell, 36 is an outgoing side polarizing plate, 37
Is a projection lens. The front polarization device 33 has the same configuration as that shown in FIG.

The light source 32 is composed of a lamp and a concave mirror, and the light emitted from the lamp is condensed by the concave mirror and is transmitted in the order of the front polarizing device 33, the incident side polarizing plate 34, the liquid crystal cell 35, and the emitting side polarizing plate 36. Then, it enters the projection lens 37. The polarization axis 38 of the entrance-side polarization plate 34 and the polarization axis 39 of the exit-side polarization plate 36 are +45 relative to the screen vertical direction 40, respectively.
And -45 °. In the pre-polarizer 33, the line 41 of intersection of the adjacent polarization-selective mirror surfaces 14 has an incident-side polarization plate 3
It is arranged so as to be perpendicular to the polarization axis 38 of No. 4.

When natural light from the light source 32 is incident on the pre-polarizer 33 along the optical axis 31, a strong P component 42 and a weak S component 43 are emitted along the optical axis 31 and are oblique to the optical axis 31. A strong S component is emitted in the direction. If the pre-polarizer 33 and the incident side polarization plate 34 are separated from each other, this strong S component is
It does not enter the incident side polarization plate 34. The P component 42 is transmitted through the incident side polarizing plate 34 with the maximum transmittance, and the S component is absorbed by the incident side polarizing plate 34. Compared with the case where the front polarizing device 33 is not used, the amount of light absorbed by the incident side polarizing plate 34 is significantly reduced, so that the amount of heat generation is reduced and the incident side polarizing plate 34 is reduced.
Temperature rise is suppressed. Further, the temperature rise of the liquid crystal cell 35 is also suppressed. As a result, the reliability of the incident side polarization plate 34 and the liquid crystal cell 35 is improved.

Since the polarizing device of the present invention is thin in the direction of the optical axis, there are less restrictions on the location of the polarizing device in the projection display device. For example, a plane mirror and a front polarizing device 33 can be arranged between the light source 32 and the liquid crystal cell 35, and the projection display device can be made compact by using the plane mirror.

It is possible to use a halogen lamp, a xenon lamp, or a metal halide lamp as the lamp of the projection display device. The prism-junction type polarization beam splitter cannot be arranged near the light source because the adhesive used for the junction changes its color when the temperature rises. However, in the polarizing device of the present invention, the glass substrate and the optical thin film have good heat resistance, and since an adhesive is not used, the polarizing device can be arranged close to the light source.

When a liquid crystal display device is used as the light valve, in order to make the image quality of the projected image symmetrical, as shown in FIG. 8, the polarization axes of the incident side polarization plate 34 and the emission side polarization plate 36 are adjusted. Generally, 38 and 39 are + 45 ° and −45 ° with respect to the screen vertical direction 40. In this case, the outgoing light from the pre-polarization device 33 needs to efficiently pass through the incident-side polarization plate 34, so the pre-polarization device 3
Each side surface of 3 is inclined by 45 ° with respect to the vertical direction 40 of the screen. This makes it difficult to compact the entire set. In order to make the set compact, it is desirable that each side surface of the front polarization device 33 is oriented in the screen vertical direction and the screen horizontal direction.

For this purpose, as shown in (FIG. 9), it is advisable to dispose a half-wave plate 43 immediately before the incident side polarization plate 34. Linearly polarized light 44 directed in the vertical direction to the screen is emitted from the front polarization device 33, and the half-wave plate 43 has its fast axis 45.
Is oriented in a direction of 22.5 ° with respect to the screen vertical direction 40. When the linearly polarized light 44 from the front polarizer 33 enters the half-wave plate 43, the linearly polarized light whose polarization plane is oriented at 45 ° with respect to the vertical direction of the screen is emitted. It penetrates the plate 34. The half-wave plate 43 is
The direction of the fast axis or the slow axis may be arranged so as to bisect the direction of the P-polarized component 44 emitted from the pre-polarizer 33 and the direction of the polarization axis 38 of the incident side polarization plate 34. .. The half-wave plate is such that when the linearly polarized light directed to the fast axis and the linearly polarized light directed to the slow axis are incident at the same phase, the phase difference between the two becomes ½ wavelength at the exit surface. .. In the configuration of (FIG. 9), since the spectrum of the light emitted from the light source 32 is wide, it is impossible to reduce the phase difference to ½ wavelength at all wavelengths, but the phase difference is high in the green spectrum with high visibility. 1
It seems that there is no practical problem if the wavelength is set to / 2.

Another embodiment of the projection type display device of the present invention will be described below. (FIG. 10) shows its configuration, in which 61 is a light source, 62 is a front polarization device, 66,
67 and 68 are 1/2 wavelength plates, 69, 70 and 71 are incident side polarization plates, 72, 73 and 74 are liquid crystal cells, and 75, 76 and 7
Reference numeral 7 is an exit side polarization plate, and 81 is a projection lens. The pre-polarizer 62 is the same as shown in (FIG. 6).

The light source 61 emits light containing color components of three primary colors of red, green and blue. The light from the light source 61 is the front polarization device 6
It is incident on 2 and linearly polarized light oriented in the vertical direction of the screen is emitted. The linearly polarized light enters a color separation optical system that is a combination of dichroic mirrors 63 and 64 and a plane mirror 65 and is separated into three primary color lights. The respective primary color lights are field lenses 66, 67, 68, half-wave plates 69, 70,
71, incident side polarization plates 72, 73, 74, liquid crystal cell 75,
76, 77 and the outgoing side polarization plates 78, 79, 80 are transmitted in this order. The light emitted from each of the emission side polarization plates 78, 79, 80 is dichroic mirrors 81, 82 and a plane mirror 83.
After being combined into one light by the color combining optical system in which the light is combined, the light is incident on the projection lens 84. Also in this case, the half-wave plates 69, 70, 71 are arranged so as to transmit the incident-side polarization plates 72, 73, 74 with the maximum transmittance.
The front polarization device 62 emits light close to linearly polarized light along the optical axis 60, and unnecessary polarization components are emitted obliquely along the optical axis 60. From the front polarizing device 62 to the incident side polarizing plate 72,
Since the distances to 73 and 74 are long, unnecessary polarization components emitted from the front polarization device 62 are incident side polarization plates 72, 73 and 7
4 does not enter, so the incident side polarization plates 72, 73, 74
Of the incident side polarization plates 72, 73, 74 is suppressed. Further, since the front polarizing device 62 has good heat resistance, the front polarizing device 62 can be arranged close to the light source 61, and since the front polarizing device 62 is thin, the set can be compacted.

Further, in the structure shown in FIG. 10, the S component obliquely emitted from the front polarizing device 62 may enter the incident side polarizing plate 73, and the heat generation of the incident side polarizing plate 73 may increase. is there. In this case, the front polarization device 62 is rotated by 90 ° from the state shown in FIG. 10 so that the direction of the P component emitted from the front polarization device 62 is parallel to the vertical direction of the screen. Good to do. By doing so, heat generation of the incident side polarization plate 73 is suppressed. Further, the S component emitted obliquely from the front polarization device 62 may be absorbed by the inner wall of the housing of the color separation optical system.

Although the liquid crystal display device is used as a light valve in the above embodiments, an optical image is formed as a change in optical rotatory power or birefringence according to a video signal such as an electro-optical crystal, and at least an incident light is incident. If a polarizing plate is used on the side, it can be used as a light valve.

[0058]

As described above, since the polarizing device of the present invention has the optical thin film attached to the glass substrate, it is inexpensive, excellent in heat resistance and light resistance, and moreover, polarized light selection which forms an oblique air layer. Since it is a prism type with a reflective mirror surface, it is possible to provide a thin polarizing device, and by using this polarizing device, the reliability of the incident side polarizing plate is improved, so that it is bright and has high image quality for a long time. It is possible to provide an inexpensive and compact projection-type display device capable of displaying the projection image of, and it is very effective.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the reflectance and the incident angle of a polarization selective mirror.

FIG. 2 is a configuration diagram of an embodiment of a polarizing device of the present invention.

FIG. 3 is a schematic configuration diagram showing a configuration of a polarization selective mirror.

FIG. 4 is a characteristic diagram showing spectral transmittance characteristics of the polarizing device of the present invention.

FIG. 5 is a schematic configuration diagram showing the configuration of another embodiment of the polarizing device of the present invention.

FIG. 6 is a schematic configuration diagram showing the configuration of another embodiment of the polarizing device of the present invention.

FIG. 7 is a schematic configuration diagram showing the configuration of another embodiment of the polarizing device of the present invention.

FIG. 8 is a perspective view showing the configuration of an embodiment of the projection display device of the present invention.

FIG. 9 is a perspective view showing the configuration of another embodiment of the projection display device of the present invention.

FIG. 10 is a schematic configuration diagram showing the configuration of another embodiment of the projection display device of the present invention.

FIG. 11 is a schematic configuration diagram of a conventional projection display device.

[Explanation of symbols]

 11 incident side prism 12 emission side prism 13 air layer 14 polarization selective mirror surface 33 polarizing device 34 incident side polarizing plate 35 liquid crystal cell 36 emission side polarizing plate 37 projection lens 62 polarizing device 72, 73, 74 incident side polarizing plate 75, 76,77 Liquid crystal cell 78,79,80 Emission side polarizing plate 84 Projection lens

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03B 33/12 7316-2K

Claims (21)

[Claims] 1. An incident-side prism that obliquely emits light after being incident substantially vertically, and an outgoing-side prism that emits light that is obliquely incident to the air layer from the incident-side prism and then substantially vertically exits. The incident-side prism and the exit-side prism are provided with optical thin films having a refractive index higher than that of the incident-side prism and the exit-side prism on their respective surfaces forming the air layer. A polarization device in which each of the polarization selective mirror surfaces is tilted with respect to the optical axis so that the transmittance becomes substantially maximum for P-polarized light incident along a predetermined optical axis as a mirror surface. 2. The refractive index in air is n ₀ , the refractive index of the optical thin film is n ₁ , the refractive index of the prism is n ₂ , the film thickness of the optical thin film is d, the exit angle to the air layer, or the air layer. Angle of incidence from θ
₀ , the refraction angle in the optical thin film is θ ₁ , the incident angle from the prism to the optical thin film surface, or the refraction angle from the optical thin film surface into the prism is θ ₂ , the main wavelength in air is λ The polarizing device according to claim 1, wherein the following conditions are satisfied. [Equation 1] [Equation 2] 3. The polarizing device according to claim 1, wherein the optical thin film has a refractive index of 2.0 or more. 4. The polarizing device according to claim 1, wherein the optical thin film is one of titanium dioxide, cerium dioxide and zinc sulfide. 5. An incident-side prism that obliquely exits after light is incident substantially vertically, at least one plane-parallel plate that forms an air layer on adjacent surfaces and on both sides, and light is emitted from the air layer. An incident-side prism that obliquely enters and then exits in a substantially vertical direction. The incident-side prism, the parallel plane plate, and the exit-side prism form at least two air layers on the incident side. A polarization selective mirror surface is formed by attaching an optical thin film having a refractive index higher than that of the prism, the parallel plane plate, and the exit side prism, and the transmittance of P polarized light incident along a predetermined optical axis is substantially the same. A polarization device in which the respective polarization-selective mirror surfaces are tilted with respect to the optical axis so as to maximize. 6. The refractive index in air is n ₀ , the refractive index of an optical thin film is n ₁ , the refractive index of a prism or a plane-parallel plate is n ₂ , the film thickness of the optical thin film is d, and the emission angle to an air layer. , The incident angle from the air layer is θ ₀ , the refraction angle in the optical thin film is θ ₁ , the incident angle from the prism or the plane-parallel plate to the optical thin film surface, or the optical thin film surface is the prism or the parallel surface. The polarizing device according to claim 5, wherein the following conditions are satisfied, where the angle of refraction into the plane plate is θ ₂ , and the dominant wavelength in air is λ. [Equation 3] [Equation 4] 7. The polarizing device according to claim 5, wherein the optical thin film has a refractive index of 1.7 or more. 8. A plurality of incident-side prisms, which are obliquely emitted after light is incident substantially vertically, and a plurality of light, which are emitted from the incident-side prism to an air layer, are obliquely incident and subsequently emitted substantially vertically. The air layer formed by a plurality of incident side prisms and the output side prism is arranged so that the cross section has a zigzag shape, and the incident side prisms are formed on the respective surfaces forming the air layer. And an optical thin film having a refractive index higher than that of the exit-side prism is attached to form a polarization-selective mirror surface so that the transmittance becomes substantially maximum for P-polarized light incident along a predetermined optical axis. A polarization device in which each of the polarization selective mirror surfaces is inclined with respect to the optical axis. 9. The refractive index in air is n ₀ , the refractive index of the optical thin film is n ₁ , the refractive index of the prism is n ₂ , the film thickness of the optical thin film is d, the exit angle to the air layer, or the air layer. Angle of incidence from θ
₀ , the refraction angle in the optical thin film is θ ₁ , the incident angle from the prism to the optical thin film surface, or the refraction angle from the optical thin film surface into the prism is θ ₂ , the main wavelength in air is λ The polarizing device according to claim 8, wherein the following conditions are satisfied. [Equation 5] [Equation 6] 10. The polarizing device according to claim 8, wherein the optical thin film has a refractive index of 2.0 or more. 11. The polarizing device according to claim 8, wherein the optical thin film is one of titanium dioxide, cerium dioxide and zinc sulfide. 12. A plurality of incident-side prisms that obliquely exit after light is incident substantially vertically, a plurality of parallel plane plates that form air layers adjacent to each other, and light is oblique from the air layers. And at least two air layers formed by the plurality of incident-side prisms, the parallel flat plate, and the emitting-side prism have a zigzag cross section. And the polarization prism surface is formed by attaching an optical thin film having a refractive index higher than that of the incident-side prism, the parallel plane plate, and the exit-side prism to each surface forming the air layer. A polarizing device in which each of the polarization selective mirror surfaces is inclined with respect to the optical axis so that the transmittance of the P polarized light incident along the predetermined optical axis becomes substantially maximum. 13. The refractive index in air is n ₀ , the refractive index of an optical thin film is n ₁ , the refractive index of a prism or a plane-parallel plate is n ₂ , the film thickness of the optical thin film is d, and the emission angle to an air layer is set. , Or the incident angle from the air layer is θ ₀ , the refraction angle in the optical thin film is θ ₁ ,
The incident angle from the prism or the plane parallel plate to the optical thin film surface, or the refraction angle from the optical thin film surface into the prism or the plane parallel plate is θ ₂ , the main wavelength in air is λ, the following conditions: The polarizing device according to claim 12, which satisfies: [Equation 7] [Equation 8] 14. The polarizing device according to claim 12, wherein the optical thin film has a refractive index of 1.7 or more. 15. A light source, a polarizing device for extracting substantially linearly polarized light from the light emitted from the light source, a light valve having a polarizing plate on at least an incident side, and an optical image formed on the light valve is enlarged and projected on a screen. 15. The projection device according to claim 1, wherein the polarization device is the polarization device according to any one of claims 1 to 14, and the light emitted from the polarization device is transmitted through the incident side polarization plate at substantially the maximum transmittance. Projection display device. 16. The projection display device according to claim 15, wherein the light valve is a liquid crystal display device. 17. A light emitting device is provided 1 in front of a light-incident side polarizing plate of a light valve.
/ 2 wavelength plate is arranged, the direction of the polarization axis of the incident side polarization plate is approximately 45 ° with respect to the vertical direction of the screen, and the polarization device has the central polarization plane of the substantially linearly polarized light emitted in the vertical direction of the screen or 16. The projection display device according to claim 15, wherein the half-wave plate is arranged so as to be oriented in the horizontal direction of the screen, and the emitted light of the polarizing device is transmitted through the incident-side polarization plate at substantially the maximum transmittance. 18. A light source that emits color components of three primary colors, a polarizing device that extracts substantially linearly polarized light from light emitted from the light source, and a color separation unit that decomposes output light from the polarizing device into three primary color lights. And three light valves having a polarizing plate on at least an incident side into which the output light from the color separation means is incident, and a projection lens for enlarging and projecting an optical image formed on the light valve onto a screen, The polarizing device is the polarizing device according to any one of claims 1 to 14, wherein the outgoing light of the polarizing device is transmitted through the incident side polarizing plate at substantially the maximum transmittance. 19. The projection display device according to claim 18, wherein the light valve is a liquid crystal display device. 20. Immediately before the incident side polarization plate of the light valve, 1
/ 2 wavelength plate is arranged, the direction of the polarization axis of the incident side polarization plate is approximately 45 ° with respect to the vertical direction of the screen, and the polarization device has the central polarization plane of the substantially linearly polarized light emitted in the vertical direction of the screen or 19. The projection display device according to claim 18, wherein the half-wave plate is arranged so as to be oriented in the horizontal direction of the screen, and the light emitted from the polarizing device is transmitted through the incident-side polarization plate at a substantially maximum transmittance. 21. The projection display according to claim 18, wherein the optical axes passing through the screen centers of the three light valves are on the same plane, and the plane of polarization of the linearly polarized light emitted from the polarization selective mirror is perpendicular to the plane. apparatus.